Solar question

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I'm thinking about replacing my old but faithful Gloworm 85-100 with a new combi to save some money on gas bills. Had a thought about keeping the old cylinder, heating it from solar collectors and using it to supply the new combi. Will this work?
 
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Not as you describe, but there are ways of using solar heated water to boost the DHW performance of a combi. However I don't think any of them could use your existing cylinder (unless modified), so it's going to be a very expensive option to pursue with a poor rate of return.
 
you need quite a well insulated cyclinder to start with. It you are going to pre heat the water feeding your combi then it will have to be a unvented as it will be mains pressure. I installed a Wolf combi onto a solar system that was preheated via a unvented and it works fine. If you are going to splash out for cylinders and boilers you might as well do it the proper way and get a dual coil unvented solar cylinder and a system boiler. Don't expect massive savings tho as it will only save you between 50% -60% on your yearly DHW gas bill ( not including your CH)
 
Is there any reason why you can't use a lift pump and an expansion vessel to stabilise the output? A lot cheaper than an unvented cylinder.

I think that if we are serious about renewable energy then we don't want to be selling people the most expensive of everything in the name of energy saving. We need to find a method which will save money.

Just maybe a cheap bog standard bs1566 cylinder to preheat a combi is the answer? The combi would only cut in when the water temperature is insufficient.

I know Alpha already make a hybrid system (is it an integral storage?), and the rest will certainly follow.
 
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Paul is right, you could boost the pressure from the cylinder with a pump to bring it to a level suitable to feed the combi, but you'd have to be sure that the initial flow at low pressure was sufficient to trigger the pump flow switch (unless Paul has something more sophisticated in mind?).

You could also look at a conversion of the cylinder to a heat store - existing coil connected to the solar panels and a new coil fitted higher up, perhaps via the immersion heater boss, to pre-heat the mains pressure cold before it feeds into the combi.

I still don't think it's worth the bother and expense.
 
I would propose a seperate flow switch, but I haven't tried my system yet, the parts have been on back order from Antares for about 6 weeks now. I'll let you know how it turns out. Reliability could be an issue, it's uncharted teritory for me.

Similar system to the self refilling sealed central heating primary system, via break tank pressure switch and pump. For that how does it sound to you if I set two pressure wsitches, one at 0.7 bar the purpose of which is to cut off the pump should there be a massive loss of pressure caused by a burst pipe or inadvertent open end, the other set at 1 bar to top the system up under normal conditions.

Paul
 
I read somewhere this weekend that the amount of energy used to create the solar panels is approx 90% that produced by them over thier lifetime.
Not sure if this is true. But worrying if it is.
 
Micky p has this system so apart from wolf and alpha via the solar mixing valve most of the other combis will not accepted pre heated water above 20 deg especially water that during some periods maybe nearlly 60deg plus. before deciding what to do you need to find a boiler manufacturer that will allow this type of system to be rigged up tto their boiler
 
Thanks for all this info. have I got this right - most combis need water at mains pressure and wont accept heated water???

Although quite a few people seem to be a bit iffy about solar, I'm getting quite keen to try it. Fitting a new boiler with a bit of fiddling around is going to cost about £2,500. There's an ebay shop selling a vacuum tube collector, twin coil cylinder, controller and pump for £690. I reckon for £2,500 outlay I could keep my old boiler which is still working, just inefficient, buy his system with another two or three collectors and still maybe have change from £2,500 if I fit most of it myself. The biggest snag I can see with solar is that you probably need a lot of hot water in early in the morning, when it's not goinfg to be doing anything. Spose we'll just have to stay in bed for a bit longer then.
 
First combis dont need mains pressure but do require a minimumdepending on make and model.

second, most combis on the market dont accept preheated water(some exceptions)

People with solar tend to have to adjust their water usage slightly to get the best gain. after a long days sun the cylinder is likely to be full of piping hot water which means evening bathtime will be using the water generated by solar, if not totally used should with a good cylinder stay warm enough for the morning ablutions but may need to apply secondary heating.

Cylinder size should be 1.5-2 times larger than already to allow for the hot water from solar plus enough water to supply all your needs heated the conventional way. normall usage is calculated at between 35-50litres per person. therefore a 120 l cylinder with solar added would need to be 210l. Big difference in size so make sure you have the room.

Panels on ebay are cheap but make sure you can get the same for the others, all panles join differently together.

Solar is easy to fit just remeber some solar manufacturers insist on the joints being either brazed or compression due to high glycol temperatures during stagnation. so unleaded solder is not always allowed.
Lee
 
Paperspace said:
Thanks for all this info. have I got this right - most combis need water at mains pressure and wont accept heated water???

Although quite a few people seem to be a bit iffy about solar, I'm getting quite keen to try it. Fitting a new boiler with a bit of fiddling around is going to cost about £2,500. There's an ebay shop selling a vacuum tube collector, twin coil cylinder, controller and pump for £690. I reckon for £2,500 outlay I could keep my old boiler which is still working, just inefficient, buy his system with another two or three collectors and still maybe have change from £2,500 if I fit most of it myself. The biggest snag I can see with solar is that you probably need a lot of hot water in early in the morning, when it's not goinfg to be doing anything. Spose we'll just have to stay in bed for a bit longer then.
In mid summer the sun comes up at approx 5am so with 3 hours early low sun shine it could have a chance of being warm. even if it isn't warm it is less work for the boiler to do. The facts are it cuts your yearly DHW energy bill by 50% to 60% on an average family home here in the UK.
 
lcgs said:
Micky p has this system so apart from wolf and alpha via the solar mixing valve most of the other combis will not accepted pre heated water above 20 deg especially water that during some periods maybe nearlly 60deg plus. before deciding what to do you need to find a boiler manufacturer that will allow this type of system to be rigged up tto their boiler

i believe this is a problem with many combis on the market. This was a job Wolf boilers passed onto us as they sold this guy the boiler to do this specific job. They reckon there boiler is one of a few that is capable of taking pre heated hot water and if it only needs rasing 5 deg c then it will. So they told us anyway.
 
To the OP.

You could feed your new combi from your existing system by heating the cylinder with the solar opanel and preheating the combi water using the original heating coil. Not many manufacturers will approve though!

This will not be that ideal but will not cost any more apart from the panels and a circulating pump.

I would add a thermostat and set it to ensure the pump only circulated the solar water when the cylinder water was below 35 C at the top of the coil and the panel output was above 35 C.

The cylinder would need to be open vented and arranged with an F&E above the solar panels.

I would also set the boiler to a lower minimum power to accept a warmer inlet without cutting out.

Be aware that I can do these things safely and not all others will be able to do so.

Tony
 
The main problem with solar is stagnation. this is where the pump stops and the fluid turns to steam, by ensuring that the water in the cylinder is at low temps all the time your system will stagnate very quickly.Stagnation causes abreakdown of the glycol mix which you will have to change more frequently.
 
i wouldn't advise an open vent solar system. I know there are some out there but it is far more safe when they are sealed. Some solar panels can reach well over 200deg C in a sealed system when in stagnation. Glycol starts to boil at 140deg C in a sealed system so if it is open vent i can see your attic being full of steam quite often. As for controling the solar pump ,most operate on a 6 deg difference then they turn on. You need some accurate thermistors to tell you the temps.
 

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